Japanese patent application No. P1998-58527 includes a description on a biaxially drawn, blow-molded bottle made of a polyethylene terephthalate resin (hereinafter referred to as PET bottle) and used for the beverage products, such as tea and fruit juices, and the like, which require a filling operation at a high temperature or a thermal treatment process. The so-called heat-resistant neck has high thermal deformation resistance strengthened by the thermal crystallization treatment, and is used as the neck of the PET bottle which is to be filled with tea, fruit juice, liquid seasoning and the like at a high temperature, or is subjected to a thermal treatment process.
FIG. 10 shows a typical PET bottle to be filled with tea, fruit juice, and the like. FIGS. 11 and 12 show a typical heat-resistant neck 20. The entire neck is in the whitened state as a result of the thermal crystallization treatment. Under the thread ridge 22 there is a bead ring 24, which is jointly used with a pilfer-proof cap to prevent the bottle from being opened by improper handling or by malfunction. The heat-resistant neck has also a neck ring 25. The mesh hatching over the heat-resistant neck 20 in FIGS. 11 and 12 shows the neck in the whitened state caused by the thermal crystallization. (This hatching is omitted in FIGS. 10.)
Meanwhile, Japanese patent application No. P1995-267235 has a description on the PET bottle to be used for carbonated beverages. FIG. 7 is an entire view of a typical PET bottle to be used for carbonated beverages. FIGS. 8 and 9 show a typical example of the so-called pressure-tight neck 10 of the PET bottle shown in FIG. 7.
The pressure-tight neck 10 of the PET bottle shown in FIGS. 7, 8, and 9 is not thermally crystallized, and therefore, is in a clear state. The bottle comprises body 17 in a cylindrical shape and bottom 18 in the so-called petaloid shape, in which multiple legs 18a are projected downward to improve the pressure-resisting property of the bottle. The pressure-tight neck 10 is provided with an intermittent thread ridge 12, which has missing portions in between the segments of the thread ridge. These missing portions 12a are used as the gas venting grooves to allow the inner pressure of carbon dioxide gas to escape through the grooves when the bottle is uncapped.
In recent years, utilization of PET bottles has been expanding in various applications, and there is a need for a neck having both the heat-resisting property and the gas-venting property, rather than the neck having either property.
For instance, a PET bottle having the heat-resistant neck is used for filling the contents at a high temperature or is treated at a high temperature for pasteurization. Then, when the bottle is left to cool to room temperature, the bottle inside is under a reduced pressure. Sometimes the round wall of the bottle caves in, and the bottle deforms. (In many cases, the bottle is provided with deformable vacuum-absorbing panels in the portions of body walls to absorb the reduced pressure. See the vacuum-absorbing panel 27a in the body wall 27 in FIG. 10.) In the heat-resistant neck 20, there has been no mechanism corresponding to the gas-venting groove, such as the missing portions 12a in the intermittent thread ridge 12 of the pressure-tight neck 10. As a result, outside air bursts into the bottle at the moment when the bottle is uncapped, and the contents spout out under the effect of the force with which the bottle recovers from the reduced pressure condition. The spillover may happen to spoil the clothes.
Even with uncarbonated contents, such as fruit juices, there are still cases where the contents fall into a pressurized condition because of gas evolution due to a change over time. In such a case, there is a fear that the contents may spout out when the cap is removed from the heat-resistant neck 20.
The pressure-tight PET bottles for carbonated beverages, such as shown in FIG. 7 are finding more and more applications that require a pasteurization process using hot shower at a high temperature, which process is conducted after the bottles have been filled with beverages. Therefore, there is a need for the neck having a heat-resistant property and also a mechanism corresponding to the gas-venting groove found in the pressure-tight neck, to deal with the above-described problem of the contents that spill over or spout out of the bottle. In the case of the pressure-tight neck 10 having the missing portions 12a in the thread ridge, the problems caused by the missing portions 12a include undesired deformation due to thermal crystallization. As the neck is deformed, the screw engagement with the cap gets out of order, and the sealing property of the bottle decreases greatly.
The above problems are attributable to the differences in the resin flow and in the cooling/solidifying behavior observed between the intermittent thread ridge 12 and the missing portions 12a during the injection molding process. It is considered that due to these differences, surface sinks inevitably occur on the top surface of the neck 10 at places corresponding to the positions of the missing portions 12a. In addition, the neck would have a shape distorted from the circular shape.
As another problem, there occur similar surface sinks also on the top surface of the neck at the place corresponding to the vicinity of the starting and ending points of the intermittent thread ridge 12.
The thickness of the round wall 11 of the pressure-tight neck 10 is also a factor affecting the extent of undesired deformation, such as the above-described surface sinks. This deformation can be inhibited by increasing the thickness. However, from the aspects of productivity, cost reduction, and resources saving of the PET bottles, it is still difficult in reality to inhibit this undesired deformation within a practical range of the thickness.
This invention has been made to solve the above-described problems. The technical object of this invention is to provide a neck having a gas-venting structure and a structure capable of controlling surface sinks and deformation caused by thermal crystallization. Thus, the object of this invention is to provide a highly safe neck that can be used widely in the field of heat-resistant containers, pressure-tight containers, and heat-resistant and pressure-tight containers.